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Certificate types

Here you can find information about the certificate types available at KTH.

What certificate types are available?

At KTH the types of server certificates you can use are

  • Primarily: "GÉANT OV Multi-Domain" (Multi-domain) – use 2048 and SHA256 (see below)
    • This certificate type allow a number of SANs (Subject Alternate Names) to be used, i.e. additional names that refer to the same server.
  • There is also Extended Validation (EV) certificates. However, these should only be used for very important services. Contact
  • Normally wildcard certificates (* are not permitted, but if you have a special use case, please contact

The certificate types are described at

Why standardize on key length 2048 rather than 4096?

As larger keys are more secure, they also generate a larger load on and worse performance of servers and other hardware.

According to NIST, a key length of 2048 corresponds to 112 bits of symmetric encryption, and should be secure until 2030.

The difference between 2048 and 4096?

  • Strength is exponentially increased, using 4–7 times more CPU.
  • Signing is slower.
  • Establishing connections (handshakes) becomes significantly slower and uses more CPU during the handshake.
  • Fewer simultaneous SSL connections can be used to a web server (or cluster).
  • Compatibility issues with 3rd party products that do not support larger keys than 2048 bits.

Performance of a server can be tested using the command

  openssl speed rsa

As an example, from a computer with an Intel i7-4770S, i.e. 4 core CPU running at 3.1 GHz:

  sign verify sign/s verify/s

rsa  512 bits 0.000114s 0.000011s 8785.3 94943.8

rsa 1024 bits 0.000632s 0.000033s 1581.7 29878.7

rsa 2048 bits 0.004090s 0.000127s  244.5 7843.4

rsa 4096 bits 0.030865s 0.000483s   32.4 2068.5